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Our Home: Earth, a Unique Life Sustaining Planet - Magnetic field of the Earth

Grade 8CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Earth behaves like a massive spherical magnet surrounded by a magnetic field called the Magnetosphere.

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The magnetic field is generated by the Geodynamo effect, caused by the movement of molten iron and nickel in the Earth's liquid outer core.

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The Magnetic North Pole is actually a magnetic south pole (physically), which is why the north end of a compass needle is attracted to it. It is located near the Geographic North Pole.

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The Magnetic Axis (the line joining the magnetic poles) is tilted at an angle of approximately 11.5∘11.5^{\circ} with respect to the Geographic Axis (the axis of rotation).

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The Earth's magnetic field acts as a shield, protecting the atmosphere and life from the Solar Wind (a stream of charged particles from the Sun) and cosmic radiation.

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The phenomenon of Auroras (Aurora Borealis and Aurora Australis) occurs when solar particles interact with the Earth's magnetic field near the poles.

📐Formulae

Angle of Inclination (Tilt)≈11.5∘\text{Angle of Inclination (Tilt)} \approx 11.5^{\circ}

1 Tesla (T)=104 Gauss (G)\text{1 Tesla (T)} = 10^{4} \text{ Gauss (G)}

Magnetic North Pole≠Geographic North Pole\text{Magnetic North Pole} \neq \text{Geographic North Pole}

💡Examples

Problem 1:

A hiker is using a magnetic compass to find North. If the angle between the Magnetic North and the Geographic North is 11.5∘11.5^{\circ}, what is this angle called and why is it important?

Solution:

This angle is known as the Magnetic Declination.

Explanation:

Because the Earth's magnetic axis is not perfectly aligned with its rotational (geographic) axis, there is a deviation. The value of 11.5∘11.5^{\circ} indicates the tilt between the two axes. Navigators must account for this to find the true Geographic North.

Problem 2:

Explain why the Earth's outer core is responsible for the magnetic field instead of the inner core.

Solution:

The outer core is liquid, allowing for convective motion.

Explanation:

The inner core is solid due to intense pressure. The outer core contains molten iron and nickel that flows due to Earth's rotation. This movement of conducting material generates electric currents, which in turn produce the magnetic field via the dynamo effect.

Problem 3:

If the magnetic field strength at a certain point is 0.5 G0.5 \text{ G}, convert this value to Tesla (T).

Solution:

0.00005 T or 5×10−5 T0.00005 \text{ T} \text{ or } 5 \times 10^{-5} \text{ T}

Explanation:

Since 1 G=10−4 T1 \text{ G} = 10^{-4} \text{ T}, we multiply: 0.5×10−4=0.00005 T0.5 \times 10^{-4} = 0.00005 \text{ T}. Earth's magnetic field at the surface is relatively weak, ranging from 0.250.25 to 0.65 Gauss0.65 \text{ Gauss}.

Magnetic field of the Earth Class 8 Notes & Examples